Conventionally, when attaching (inserting) a rotor with a magnet to (into) a rotor housing with a stator coil, a fixed or movable attachment apparatus is used to make the rotor movable only in the axis direction with respect to the rotor housing so as to prevent an outer circumference (magnets) of the rotor from being magnetically attached to an inner circumference to the rotor housing (for example, see Patent Documents 1 and 2).    Patent Document 1: Japanese Unexamined Patent Application, First Publication No. H07-67299    Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2002-210619